1. Field of the Invention
The present invention relates to a lens barrel having a structure for moving a lens unit with a predetermined quantity by use of a cam ring when in focusing and in zooming as well.
2. Related Background Arts
A conventional lens barrel includes a movable frame holding a focusing lens unit and moving an optical-axis direction, a fixed drum for supporting this movable frame so as to be movable in the direction of the optical axis, and a cam ring for giving a driving force for moving the movable frame. According to this type of lens barrel, when in such an optical system that a moving quantity of the focusing lens unit which quantity is needed for focusing up to a closest focusing distance is comparatively small, the cam ring can be fitted to the fixed drum while securing a sufficient length in the direction of the optical axis and can be therefore held on the fixed drum with a stability.
According to a lens barrel having a large maximum photographing magnification and therefore capable of executing, e.g., a close-up photography, however, when in such an optical system that the moving quantity of the focusing lens unit which is required for focusing up to the closest focusing distance is large, the movable frame for holding the focusing lens unit and the cam ring for moving the focusing lens unit, become elongate in the direction of the optical axis. Therefore, in the same positional relationship, the movable frame requires a space having a considerable length in the direction of the optical axis, and the cam ring can not be fitted to the fixed drum while securing the sufficient length in the direction of the optical axis, resulting in such a problem that the cam ring is stably held on the fixed drum with a difficulty.